<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <title>Title</title>
  <style>
    #d1{
      width: 200px;height: 200px;
      border: 10px inset red;
      /*设置圆角,当值大于宽高一半时为正圆(边框也占宽度)*/
      border-radius: 200px;
    }
    #d2{
      width: 100px;height: 100px;border:1px solid red;
      /*给元素添加内边距,默认会影响元素的显示范围*/
      padding-top: 50px;
      padding-left: 50px;
      /*添加以下样式后,内边距不再影响元素的宽高*/
      box-sizing: border-box;
    }
    body{
      margin: 0px;/*去掉自带的8个像素外边距,内容贴边*/
    }
    *{margin: 0;padding: 0}
    p,h3,ul{margin: 0;padding: 0}
  </style>
</head>
<body>
<p>段落标签</p>
<h3>内容标题</h3>
<input type="text">
<ul>
  <li>aaa</li><li>bbb</li><li>ccc</li>
</ul>
<div id="d2">内边距</div>
<div id="d1">边框测试</div>
</body>
</html>